This application claims the priority of German Application No. 10 2007 008 942.4 filed Feb. 21, 2007, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an injection head for the combustion chamber of a rocket propulsion unit. In particular, the invention relates to such a combustion chamber having a number of injection elements that are distributed over a base area such that propellant constituents can be injected from one outlet of the injection elements respectively into the combustion chamber. As a result, hot gas can be generated by mixing and combustion of the propellant constituents in the combustion chamber, which hot gas can be accelerated to a high velocity for generating thrust.
The propellant constituents are fed into the combustion chamber of a rocket propulsion unit by injection elements. In a liquid-fuelled rocket engine, an oxidizer and the actual fuel are required as the propellant constituents. As a result of the injection of the propellant constituents into the combustion chamber, the latter are mixed with one another and burnt, generating a hot gas at a high temperature and pressure. As a result of the expansion of the hot gas to a high velocity within the combustion chamber, the thermal energy of the hot gas is converted to kinetic energy, and thrust is generated.
The efficiency of the rocket propulsion unit depends decisively on the quality of the propellant conversion. The latter, in turn, is a function of the type of injection; for example, the number and arrangement of the injection elements in the injection head. For cryogenic propellants, such as hydrogen and oxygen, so-called coaxial injection elements are used virtually without exception. When the latter are used, the oxygen is injected into the combustion chamber by way of a central tube and an annulus arranged around the central tube. In this case, it is known to inject one of the propellant constituents with a swirl in order to improve its mixing and thereby the combustion. The use of coaxial injection elements is also known in the case of storable propellants, such as LOX/HC or MMH/NTO.
One object of the present invention is to provide an injection head for the combustion chamber of a rocket propulsion unit which has an efficiency when that is higher than that of conventional injection heads, when converting propellants.
This and other objects and advantages are achieved by the injection apparatus according to the according to the invention, which is based on the recognition that, for ideal conversion of the propellants in the combustion chamber, an infinite number of elements would be required to provide optimal distribution and mixing of propellant constituents in the combustion chamber. However, since this is not possible for practical reasons, the infinite number of injection elements, which are distributed over the base area of the injection head, forces a discrete injection. In this case, it was found that, when the propellants are injected into the combustion chamber, the propellant or the oxidizer encounters a sudden cross-sectional widening at the outlet of the injection element. This creates clearances in the combustion chamber close to the base area between the injection elements, in which clearances recirculation zones with losses are formed during the hot gas operation. The recirculation zones result in a loss of pressure, similar to “Carnot's shock loss”. Here, the pressure loss has a directly proportional effect on the loss of thrust. The base area over which the number of injection elements are arranged is also called head plate or face plate.
For avoiding this loss of pressure, in the injection head according to the invention the base area of the injection head has a contoured design, which prevents (or at least reduces) the formation of zones of reduced pressure, particularly between directly adjacent outlets. By means of the contoured base area of the injection head in the combustion chamber, the recirculation zones can be avoided, so that the above-described pressure losses are prevented or at least reduced. As a result, a higher efficiency can be achieved.
The contoured shape of the base area of the injection head is formed by a number of elevations which extend between the injection elements into the combustion chamber in such a manner that clearances between the outlets are avoided. The contouring generally depends on the geometry of the injection head, that is, on the type, size and number of injection elements as well as their distribution over the base area.
It was found to be expedient to arrange at least one elevation between two outlets respectively. In a further feature of the invention, precisely one elevation is arranged between two outlets respectively, which may be further developed to be bulged or curved, so that a cross-sectional widening for the propellant constituents exiting from the outlets of the injection elements is limited or takes place in a defined manner.
In other words, the head plate of the injection head according to the invention is constructed such that the injection elements are arranged in funnel-shaped indentations.
It is also expedient for a foot of the elevation of the contoured design to adjoin at least one of the outlets in order to provide a defined widening of the cross-section in the area of the outlets of the injection elements, and to bound a cross-sections widening so as to avoid zones with pressure losses in the combustion chamber.
According to a further aspect of the invention, an elevation is arranged between an outlet and a wall bounding the combustion chamber, so that (as described above) the formation of a recirculation zone between the combustion chamber wall and the outlet of an adjacent injection element (which would also result in a reduction of the efficiency) is also avoided.
The contoured base area can be formed in the head plate according to a further feature. This means that the contour is integrated in the head plate. Alternatively, the contouring can be deposited as an additional body onto an essentially plane head plate in which the injection elements are arranged. In this case, the contoured base area is provided by a body equipped with the desired contour, which body is then arranged on the head plate of the injection head. The contoured body may comprise metallic and/or non-metallic material, depending essentially on the thermal stress.
By providing a contoured head plate of an injection head for the combustion chamber of a rocket propulsion unit, the quality of the propellant conversion can be improved. By means of the 3-dimensional surface of the base area of the injection head, the stability behavior during the operation of the rocket propulsion unit is also improved.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.